Can a faulty capacitor affect spark quality?

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
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tippi11
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Can a faulty capacitor affect spark quality?

Post by tippi11 »

Hello experts,

During a short ride with my g3 the engine stopped without any signs of problems on the route before. Back at home, I tried to start it again for several times without any success. It is a miracle to me because fuel/carb, ignition timing and magneto (new coil winding, points) are ok. Magneto is a Lucas SR1 and there is an automatic advance/retard unit used; everything worked before as it should. And I have a spark with the spark plug removed and kick-start.
But I don’t know whether the spark “quality” is good enough to fire. Can a faulty capacitor affect the spark intensity so significantly? As per my understanding the capacitor only minimizes burn effects on the points, but has no direct impact on spark intensity.

Thank you very much for any hints and guidance, Peter.
SPRIDDLER
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Re: Can a faulty capacitor affect spark quality?

Post by SPRIDDLER »

tippi11 wrote: Thu Jun 17, 2021 6:07 pm .... fuel/carb, ignition timing and magneto (new coil winding, points) are ok. ......
:? hmm........
And I have a spark with the spark plug removed and kick-start.
Well if that's the case and all the rest is as good as you say I'd try a new sparkling plug as it may be failing to sparkle under compression, (although plugs rarely fail instantaneously).
Another possibility is than when the plug is out and the HT lead is in a different position to normal it has continuity, but when the plug is fitted in the head it may not. (That baffled me on one occasion). Check it has a good connection at the mag and the plug cap.
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Which taken at the flood............'
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Taid
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Re: Can a faulty capacitor affect spark quality?

Post by Taid »

Arcing at the contact breaker points leaks away power that should be going towards the production of the spark in the plug .. the capacitor reduces the arcing and so improves the spark ..

Search the net for 'what is the purpose of a capacitor in a magneto' ..
Last edited by Taid on Fri Jun 18, 2021 8:05 am, edited 1 time in total.
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Andy G
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Re: Can a faulty capacitor affect spark quality?

Post by Andy G »

Are you absolutely sure that fuel is getting to the cylinder?
Assuming that you have a spark of at least visible strength, the timing something like correct, enough compression to be felt when kicking, then the only thing missing is fuel to produce some form of reaction however imprecise.

I would eliminate this possibility first by flooding the carb, kicking a few times then removing the plug for a sniff test?

Then at least you can chase a spark to your heart's content.
Bombling contentedly around rural Aberdeenshire
Mick D
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Re: Can a faulty capacitor affect spark quality?

Post by Mick D »

Hi

To me your symptoms indicate a fuel issue, have you checked the pilot jet is clear? Are the fuel filters clear? Is the breather hole in the fuel cap clear?

Regards Mick
tippi11
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Re: Can a faulty capacitor affect spark quality?

Post by tippi11 »

Thank you very much - I will check everything as you recommended.
Yesterday night (after many hours of standing still) I had the situation that it fires once or twice, but only this very short-term bang, bang. More kicking without any success ...
Regards, Peter
Groily
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Re: Can a faulty capacitor affect spark quality?

Post by Groily »

might also be worth checking the auto-advance hasn't slipped on the taper? That would leave you with sparks that weren't much use, for being in the wrong part of the space/time continuum . . .
56G80S
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Re: Can a faulty capacitor affect spark quality?

Post by 56G80S »

Groily, are you uploading posts from the TARDIS?

Well done for not promoting your excellent BrightSpark EasyCap, but as I have no pecuniary interest, I can. Those old aluminium foil things are a pain.

Johnny B
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Re: Can a faulty capacitor affect spark quality?

Post by Groily »

Feels a bit like a parallel universe sometimes, have to say Johnny B!
But no, just passing time on a lousy wet day on terra firma franca.
Might have thought of a way of putting up a link to a website or something, but I'm not convinced this is a condenser problem. I'm more with the 'fuel' brigade, or, as I was musing, a slipped ATD which regained its tenuous grip in the wrong place. But who knows?! Fuel is often as not sparks, and sparks often enough fuel, we know this! And then, after exhaustion has set in chasing faults that aren't there, it turns out to be a tight valve clearance, or a serious catastrophe with a piston, or something! The joy of it all.
Of course, being the happy owner of only twins, I don't really have much trouble from one year to the next, they are so reliable . . :D 250-300km in the wet coming up tomorrow morning - I'll be chastened if I don't make it there and back and round and about. Why wouldn't she? With better part of half a MILLION miles on the old 500, you get used to getting where you want to go . . and back! And she's a mannered lady, she tells you discreetly if she's starting to feel unwell, and you give her an aspirin and an early night. Chippie's favourite hammer, 5 new 'eads and 4 new 'andles, but same hammer for all that . . . .
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